There is a fly that can locate a cricket from the sound it makes, despite other noises in the background. Yet the hearing mechanism that helps the fly do this spans only 1.5 mm, which is 50 times smaller than the wavelength of the cricket's chirp. Now, engineers have found a way to mimic the fly's super-hearing in a tiny device that does not require a bulky battery.
A paper describing the work is published in the journal Applied Physics Letters.
The engineers, from the Cockrell School of Engineering at the University of Texas at Austin, say the new device could be used in a new generation of hypersensitive hearing aids that use intelligent microphones to select only those sounds or conversations that the wearer wants to hear.
Fly's sophisticated hearing can locate a cricket with remarkable accuracy
Neal Hall, an assistant professor in the Cockrell School's Department of Electrical and Computer Engineering, and his team of graduate students, drew their inspiration from pioneering work by Ronald Miles at Binghamton University, NY, and Ronald Hoy at Cornell University, Ithaca, NY.
They were the first to describe the technological potential of emulating the super-hearing mechanism of the yellow-colored parasitoid fly Ormia ochracea, which stalks and locates male field crickets from their chirps and lays live larvae on and around them.
The fly can locate the cricket with remarkable accuracy because it has a sophisticated sound processing mechanism that determines the direction of the sound within an angle of 2 degrees.
Using the fly's super-evolved hearing structure as a model, Prof. Hall and colleagues made a tiny pressure-sensing device out of silicon. With a span of only 2 mm, the device is nearly the same size as the fly's hearing organ.
Unlike many insects, the reason humans and other mammals can pinpoint the source of a sound is because we have a much larger distance between our ears. The sound processing mechanism in our brains uses the time difference in the arrival of the sound at the two ears to locate the source.
But insects' bodies are generally too small to do this - the sound waves effectively hit both sides almost at the same time.
That is, except for insects like O. ochracea - it can locate the direction of a cricket's chirp even though its ears are less than 2 mm apart. Its highly evolved hearing mechanism can sense the 4 millisecond gap between the sound entering one ear and the other. It also amplifies this time difference using a "teeter-totter" or "see-saw" mechanism that allows it to locate the cricket with remarkable accuracy.
Engineers emulated fly's hearing mechanism using a flexible beam
To replicate the fly's hearing mechanism, the team made a flexible beam incorporating piezoelectric materials that allowed them to use the flexing and rotation of the beam as a way to measure sound pressure and pressure gradient at the same time.
While other teams have already tried to build hearing devices that emulate the fly's super-hearing, Prof. Neal and colleagues are the first to use piezoelectric materials, which convert mechanical pressure into electrical signals and allow the device to work with very little power.
"Because hearing aids rely on batteries, minimizing power consumption is a critical consideration in moving hearing-aid device technology forward," says Prof. Hall.
He sees this technology being attractive to people with hearing problems in the future. While as many as 1 in 10 Americans could benefit from a hearing aid, currently only a fifth of this number use one, he adds.
He says many believe the main reason for the gap is hearing aid wearers' dissatisfaction with the devices:
"Turning up the volume to hear someone across from you also amplifies all of the surrounding background noise - resembling the sound of a cocktail party."
As well as taking hearing aid technology to a new level, the device could also be useful in military and defense applications. For example, in dark environments where visual cues are absent.
Funds from the Defense Advanced Research Projects Agency (DARPA) helped finance the study.
In February 2014, Medical News Today reported how researchers have developed a new low-powered chip that offers the prospect of cochlear implants without external hardware.